Energetic protective coating for caseless ammunition

ABSTRACT

Caseless ammunition comprising propellant components provided with an energetic thermal and moisture-resistant coating are characterized by good environmental protection. The employment of a high temperature resistant explosive as a component of the coating permits the application of relatively thick coatings to obtain the advantage of increased thermal resistance without a consumability accommodation in the ballistic cycle.

11mm States afienfi 1191 g [1 1 3,73,@@% Qninian 51 May 1, 1973 i [54]ENERGETIC PROTECTIVE COATING 3,504,630 4/1970 Picard ..149/93 x FORCASELESS AMMUNITION r Prima Examiner-RobertF Stahl 751 t: 0sehB.ulPhldlh,P. 1 or J Q m 1 a e p a Attorney-Harry M. Saragovitz, Edward J.Kelly, Her- [73] Ass1gnee: The United States of America as be Berland Db ff represented by the Secretary of the Army 7 57 ABSTRACT [22] Flled:June 1970 Caseless ammunition comprising propellant com- [21] Appl. No.:45,743 ponents provided with an energetic thermal and moisture-resistantcoating are characterized by good 52 us. (:1. ..102/38, 102/43 P,lO2/DlG. 1 envimnmemal Protection The employment Of a high 51 1m. (:1..F42b 5/18 temperature resistant explosive as a component of the 58Field of Search ..l02/38, DIG. 1,43, Coating permits the application ofrelatively thick 102/39; 149/2 coatings to obtain the advantage ofincreased thermal resistance without a consumability accommodation in [56] References Cited the ballistic cycle.

UNITED STATES PATENTS 3 Claims, 1 Drawing Figure 2,966,405 12/1960 Sloan149/92 3,397,637 8/l968 Bobinski et al. ..lO2/DIG. l

Patented May 1, 1973 3,730,094

INVENTOR, JOSEPH B. QUINLAN ATTORNEYS:

ENERGETIC PROTECTIVE COATING FOR CA'SELESS AMMUNITION The inventiondescribed herein may be manufactured, used, and licensed by or for theGovernment for governmental purposes without the payment to me of 5 anyroyalty thereon.

BACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION This inventionrelates to a protective coating for caseless ammunition andparticularly, to a thermaland moisture-resistant coating for caselessammunition which provides good environmental protection. Moreparticularly, the invention relates to caseless ammunition componentsprovided with'energetic environmental protective coatings.

2. DESCRIPTION OF THE PRIOR ART Caseless ammunition, i.e., ammunitionhaving a consumable or combustible cartridge case is well known and theadvantages thereof vis-a-vis cased rounds are discussed at length in theprior art, e.g., U. S. Pat. No. 2,982,211. (Beal et al.), issued May 2,1961 and U. S. Pat. No. 3,212,440 (Quinlan et al.) issued Oct. 19, 1965.In general these advantages comprise a considerable saving in ammunitionweight, obviation of the case disposal problem, increased weapon firingrate potential and weapon weight attributable to elimination of theejection operation and mechanism, and elimination of the need forexpensive cartridge case metals and metal forming operations as well asthe need for stockpiling such metals to avoid critical shortages.

The concept of a caseless cartridge is not of recent vintage, asevidenced by the disclosure of British Pat. No. 7193 AD. 1891. TheBritish specification sets forth the generally accepted criteria that acaseless cartridge consist essentially of a cartridge body or rigidcharge formed of any suitable explosive substance and that such body orcharge be completely consumable and constitute either the whole or apart of the propulsive charge.

Since the original concept, improvements in the design and fabricationof caseless ammunition have been the subject of numerous patents. Forexample, Beal et al., infra, disclose caseless cartridges providingmeans for the appropriate attachment of projectiles and primer caps andpossessing mass burning rate and ballistic characteristics comparable tothose possessed by metal cased rounds of similar caliber and propellant.

' While progress in the development and improvement of caselessammunition is borne out by the aforementioned discussion, a particularlyvexing problem has attended the use of such ammunition from the outsetand has continued to plague investigators in their attempts to provide asolution therefor. This problem relates to environmental protection forcaseless ammunition and is basically concerned with imparting thermaland moisture resistance to caseless cartridges. While. recognitionof theproblem is not original, prior art attempts have not been whollysatisfactory. In the main, they have provided only partial environmentalprotection while concomitantly compromising the ballistic performancecharacteristics of the caseless cartridges. In this regard, the Britishspecification, infra, discloses coating the exterior surface of acaseless cartridge with e an incombustible material, such as paraffin orasbestos cloth, to improve thermal resistance and, accordingly,

necessarily effects thereby an accommodation in the ballistic cycle.Beal et al, infra, suggest the application of a protective coating to alaminated combustible cartridge case for the purpose of waterproofingor, in some instances, as a means of controlling or retarding theburning rate of the combustible case, although lacking in a teaching ofa specific coating composition that will accomplish the desired results.Quinlan et al, infra, teach the application of a thin coating, not morethan 0.002 inch thick, of a suitable material to the outer surfaces ofpropellant to reduce heat conductivity from the weapon chamber to theround and thus reduce the danger of cook-off. Suggested coatingmaterials by Quinlan et al. include percent by weight of methylmethacrylate and the balance molybdenum disulfide or graphite. As theQuinlan et al. coatings are necessarily restricted to relatively thindimensions in order to insure adequate combustibility and ballisticperformance, the degree of thermal resistance afforded by such coatingsis minimal, and consequently, constitutes an unduly limiting designfactor.

SUMMARY OF THE INVENTION The present invention is concerned with anenergetic coating composition for providing caseless ammunitioncomponents with environmental protection, said composition consistingessentially of a high temperature resistant explosive.

The invention also contemplates a liquid coating mixture for applicationto caseless ammunition components to provide environmental protectivecoatings therefor, said mixture consisting essentially of a suspensionin an organic medium of an energetic composition consisting essentiallyof a high temperature resistant explosive.

The invention is further directed to a process for providing caselessammunition components with environmental protection comprising applyinga liquid coating mixture to said components to provide a wet coatingthereon, said mixture consisting essentially of a suspension in anorganic medium of an energetic composition consisting essentially of ahigh temperature resistant explosive, evaporating said organic medium,from said wet coating to obtain a dry coating, and repeating saidmixture applying and organic medium evaporating steps until a desiredcoating thickness is obtained.

The invention is also directed to a process for providing a caselessround with environmental protection comprising applying a liquid coatingmixture to the individual components thereof to provide wet coatingsthereon, said mixture consisting essentially of a suspension in anorganic medium of an energetic composition consisting essentially of ahigh temperature resistant explosive, evaporating said organic mediumfrom said wet coatings to obtain dry coatings, repeating said mixtureapplying and evaporating steps until a desired coating thickness isobtained, assembling said individual components to form said caselessround, and repeating'said mixture applying and evaporating steps withrespect to the assembled round.

The invention also relates to a caseless round characterized by improvedenvironmental protection comprising an assembly of components whereineach of said components as well as the assembled round are provided withan energetic coating composition consisting essentially of a hightemperature resistant explosive.

The underlying concept of the present invention resides in theproposition that the substitution of an energetic coating for thenon-energetic, caseless ammunition protective coating of the prior artoffers the advantage that no consumability accommodation is required inthe ballistic cycle. An added advantage stems from the thermalresistance afforded by the thicker coatings without undesirable effectson the ballistic cycle.

DESCRIPTION OF THE DRAWING The FIGURE depicts a sectional view inelevation of a small caliber caseless round coated in accordance withthe invention.

DETAILED DESCRIPTION Referring now to the single FIGURE of the drawingwherein a sectional view in elevation of a preferred embodiment of theinvention is shown, a molded propellant It) has the usual projectile 11adhesively secured in a recess thereof. The adhesive may be of anywellknown combustible type, such as Duco cement, for example, which is anitrocellulose dissolved in methyl ethyl ketone, and having nodeleterious effects upon the molded propellant. The projecle may partakeof any suitable small arms type, that shown being a typical jacketedtype for receiving the impressions of the lands and grooves to effectstabilization An axial cavity 12 if formed within the round and isgenerally centrally disposed therewithin as shown.

A primer 13 is received within an axial recess 14 of substantially thesame diameter as cavity 12 but is separated therefrom by a wall 15comprising the original integrally molded propellant. The wall 15supports primer 13 when it receives an impact from a firing pin, notshown. A coating 17, in accordance with the present invention, isapplied to the propellant components and 13 by spraying, dipping, etc. Afinal coat is also applied to the assembled round.

The primer 13 is suitable of the type disclosed in U. S. Pat. No.3,l87,67l (Scanlon et-al.) issued June 8, 1965, and containing a leadstyphnate type mix ignited by a percussion cap enclosed between thinsheets of paper. The configurations of some of the original propellantgranules are shown at 16.

The propellant composition employed in the molded propellant componentsdiscussed herein forms no part of the present invention and may be anyof the myroid of compositions typically used for caseless ammunition.Examples thereof are found in Propellant Chemistry" by Stanly F. Sarner,Reinhold Publ. Co., New York (1966), pages 108 ll 1.

A suitable technique for binding propellant granules together to formmolded caseless ammunition components is disclosed by Quinlan et al.,infra, using a binder, such as collodion comprising 5% nitrocellulose of7-l0% nitrogen content, the balance being 50-50 mixture of ethanol andethyl ether. Such a binder is less energetic than the propellantgranules and possesses a slower burning rate.

The coating composition of the present invention consists essentially ofan explosive which is resistant to high temperatures and is desirablyselected from the group consisting of nitro-organics and nitrate esters.These organic compounds incorporate oxygen into the molecule in anenergetic form and consequently, the coatings prepared therewith areregarded as energetic coatings, thatis, coatings which during the courseof the ballistic cycle have the net effect of supplying energy to thepropulsion system. The nitro-organics and particularly, the cyclicnitro-organics such as RDX and HMX are preferred explosives for theinventive coating compositions. RDX has the formula [CH NNO and is namedtrinitrotrimethylenet riamine commonly called cyclonite, while HMX hasthe formula [cl-l NNO- h and is named tetranitrotetramethylenetetramine,commonly called homocyclonited. Other suitable high temperatureresistant explosives include those described by Sarner, infra, pages 278299.

For the purpose of improving the high temperature resistance of theinventive coatings, the explosive material forming the essentialcomponent thereof is mixed with an inert material, that is, anon-energetic material which is 'consumable during the ballistic cycleand does not detrimentally affect same. Suitable materials in thisregard comprise thermoplastic polymers and copolymers of acrylic acid,butyric acid, methacrylic acid, esters of these acids, andacrylonitrile. A preferred non-energetic material is cellulose acetate.The proportion of non-energetic material employed in the coating is suchthat the minimum employed is sufficient to provide the desired thermalresistance while the maximum employed does not detract from the neteffect of supplying energy to the propulsion system. In general, thecoating may consist of parts by weight of explosive acid and up to about20 parts weight of non-energetic material.

EXAMPLE I A mixture of 20 parts by weight of cellulose acetate and 80parts by weight of RDX is prepared and added to acetone to form asuspension. The liquid mixture is then employed to provide a protectivecoating for a 7.62mm caseless round comprising a projectile, a ho]- lowcylindrical, molded propellant body and a combustible primer assembly,consisting of primer cup, primer pellet and propellant disc seal. Themolded propellant components employ nitrocellulose granules bound bycollodion as described by Quinlan et al., infra, and are coated byimmersion in the liquid mixture, the propellant body component beingprovided with a suitable plug to prevent coating of the interior wallsurfaces. Thereafter, the solvent is evaporated from the wet coatings byheating at l22F for 30 minutes. The coating procedure is repeated untila coating thickness of about 5 mils is obtained. The coated componentstogether with the projectile are then assembled to form a round and afinal coating is applied as aforementioned. The resultant round exhibitsadequate moisture resistance as evidenced by ability tobe fired afterimmersion in water. Further, the applied coating is high temperatureresistant as evidenced by an explosion temperature at least 50C.. higherthan the explosion temperature of the molded propellant.

EXAMPLE n The procedure of Example I is carried out with the exceptionthat I-IMX is substituted for RDX. Comparable results are obtained.

I wish it to be understood that I do not desire to be limited to-theexact details of construction shown and described, for obviousmodifications will occur to a person skilled in the art.

I claim: a

1. In a caseless round of ammunition having a molded propellant chargeof nitrocellulose granules and a projectile adhesively secured within aforward portion thereof, said molded propellant charge having arearwardly opening recess in a rearward end thereof,

2. The structure of claim 1 wherein said explosive is RDX.
 3. Thestructure of claim 1 wherein said explosive is HMX.